Al Bond Research Articles

First-principles calculations of the structural, mechanical, electronic and bonding properties of (CrB2)n CrAl with n = 1, 2, 3

The crystal structure, the electronic structure and the mechanical properties were investigated for (CrB2)nCrAl with n = 1, 2, 3 by using the all-electron projector augmented wave method with the Perdew-Burke Ernzerhof functional. The calculated bulk moduli for Cr2AlB2, Cr3AlB4 and Cr4AlB6 were 202, 222 and 234 GPa, respectively, and the Young moduli were estimated to be 397, 412 and 434 GPa, respectively. All three materials were identified as stiff and hard materials; however, the density of states and the projected density of states analysis predicted a metallic behavior for all investigated materials. The partially filled d-orbitals of Cr atoms have an important role in attributing metallic behavior to these materials. The hardness of these materials was related to the presence of quite strong BB covalent bonds and the metallic characteristic arises from CrCr interactions. The chemical interpretation of the physical properties was made with the electron localization function and the investigation of the topology of the electron densities was provided, based on the quantum theory of atoms in molecules. Surface properties were explored for slab models, arbitrarily chosen to be along the a-axis. The metallic behavior of the compounds (CrB2)nCrAl continues in the surface model. Using the electron localization function and Bader's charge analysis, a small increase of the number of electronic carriers was observed, due to the localization of some AlAl bonds in the slab models.

Investigation of Thermal Atomic Layer Deposited TaAlC with Low Effective Work-Function on HfO2 Dielectric Using TaCl5 and TEA as Precursors

TaAlC prepared by thermal atomic layer deposition using tantalum pentachloride (TaCl5) and triethylaluminum (TEA) is successfully demonstrated as work-function metal gate material for the first time. Detailed physical characteristics are demonstrated by X-ray photoemission spectroscopy and X-ray reflectivity. It is found that the as-deposited TaAlC film is consisted of Ta-C, Al-Al and trace Al-C bonds. The TaAlC has reasonable growth rate and linear growth without incubation. Metal-oxide-semiconductor (MOS) capacitor is used to evaluate the effective work-function (EWF). The EWF of TaAlC on HfO2 dielectric can be tunable from 4.65 eV–4.26 eV by process parameter. The lowest EWF which is close to conduction band edge is suitable for high performance FinFET application.

Comparative tensile behavior of freestanding γ-γ′ and β-(Ni,Pt)Al bond coats and effect on tensile properties of coated superalloy

The tensile behavior of freestanding 40μm thick γ-γ′ and 50μm thick β-(Ni,Pt)Al coatings was evaluated at room temperature (RT) and 870°C by microtensile testing method. Simultaneously, the effect of coatings on the tensile properties of the directionally solidified (DS) CM-247LC superalloy was also examined. Both the freestanding coatings had lower strength than that of the superalloy and the yield as well as the ultimate tensile strength (YS and UTS) of the superalloy substrate was lowered by the application of either coating. At RT, the freestanding γ-γ′ coating was significantly stronger (YS=660MPa) and ductile than that of the brittle β-(Ni,Pt)Al coating which fractured at ~300MPa with negligible ductility. Comparatively, the β-(Ni,Pt)Al coating caused more deterioration in substrate tensile properties (especially ductility) than that of the γ-γ′ coating at RT. On the contrary, at 870°C, albeit their similar YS, the γ-γ′ coating exhibited brittle intergranular fracture and limited ductility whereas the β-(Ni,Pt)Al coating showed ductile failure. Numerous sharp cracks formed by the de-cohesion of the γ and γ′ phase boundaries within the γ-γ′ coating and their penetration into the substrate aggravated degradation in the substrate ductility than in case of the ductile β-(Ni,Pt)Al coating.

Different electronic sensitivity of BN and AlN nanoclusters to SO2 gas: DFT studies

Density functional theory calculations are used to investigate the electronic and structural behavior of a pristine Al12N12 and B12N12 nanoclusters to sulfur dioxide (SO2) gas adsorption. It is found that the SO2 molecule prefers to be adsorbed on the XN (X = B or Al) bonds with the Gibbs free energy change of −58.6 and −12.2 kcal/mol on the Al12N12 and B12N12 nanoclusters at room temperature, respectively. When a SO2 molecule is adsorbed on the BN cluster, a new state appears through the HOMO-LUMO gap of the cluster which significantly reduces the gap (by about 29.8%). Thus, the electrical conductivity of the B12N12 is meaningfully increased, indicating that it can produce an electronic noise at the presence of SO2 molecules and can be used in chemical sensors. The recovery time for the SO2 desorption from the surface of BN cluster is calculated to be very short (∼0.96 m). We find that the electrical conductivity of the cluster much more increases by increasing the gas coverage and a larger electronic signal can be obtained at high concentrations. The Al12N12 shows a higher reactivity to the SO2, but its electronic properties are insensitive to this gas.

Mesoporous aluminosilicate macrospheres obtained by spray gelling technique

Porous aluminosilicate macrospheres were prepared by spray gelling technique using chitosan, chitosan and yeast cells and respectively chitosan, yeast cells and gelatin as templating agents. The removal of the template by calcination generated the hierarchical porous structure. The synthesized macrobeads were characterized by the nitrogen sorption technique, Fourier transform infrared spectroscopy, X-ray powder diffraction and scanning electron microscopy/energy dispersive X-ray analyses analyses. The scanning electron microscopy images and Brunauer - Emmett - Teller nitrogen sorption data proved that the porosity of the samples is highly influenced by the nature of the templating agent. Fourier transform infrared spectroscopy confirmed the formation of Si–O–Si and Si–O–Al bonds. The Wide angle X ray scattering patterns indicate that the samples are amorphous-crystalline materials. The ratio between the crystaline and amorphous phases is influenced by the nature of the template used to synthesis. The macrobeads were tested as adsorbents for the removal of Blue Basic 3 dye from aqueous solutions and the separation performance proved to depend strongly on the preparation procedure. The macrospheres templated with chitosan, yeast cells and gelatin were reused ten times without significant loss of adsorptive capacity.

From illite/smectite clay to mesoporous silicate adsorbent for efficient removal of chlortetracycline from water

A series of mesoporous silicate adsorbents with superior adsorption performance for hazardous chlortetracycline (CTC) were sucessfully prepared via a facile one-pot hydrothermal reaction using low-cost illite/smectite (IS) clay, sodium silicate and magnesium sulfate as the starting materials. In this process, IS clay was “teared up” and then “rebuilt” as new porous silicate adsorbent with high specific surface area of 363.52m2/g (about 8.7 folds higher than that of IS clay) and very negative Zeta potential (−34.5mV). The inert SiOSi (Mg, Al) bonds in crystal framework of IS were broken to form Si(Al) O− groups with good adsorption activity, which greatly increased the adsorption sites served for holding much CTC molecules. Systematic evaluation on adsorption properties reveals the optimal silicate adsorbent can adsorb 408.81mg/g of CTC (only 159.7mg/g for raw IS clay) and remove 99.3% (only 46.5% for raw IS clay) of CTC from 100mg/L initial solution (pH3.51; adsorption temperature 30°C; adsorbent dosage, 3g/L). The adsorption behaviors of CTC onto the adsorbent follows the Langmuir isotherm model, Temkin equation and pseudo second-order kinetic model. The mesopore adsorption, electrostatic attraction and chemical association mainly contribute to the enhanced adsorption properties. As a whole, the high-efficient silicate adsorbent could be candidates to remove CTC from the wastewater with high amounts of CTC.

Effects of Probe Marks on Shear Test of Copper Ball Bonds in Two Pad Aluminum Thicknesses

Abstract This paper continues the work of reference [1], evaluating shear test results of Cu ball bonds over a variety of probe marks in two different pad aluminum (Al) thicknesses (0.8μm and 3μm). The presence of invasive probe marks on thick Al bond pads lowers certain shear force results.. Lower values of shear force imply reduced Cu bond reliability. Physical factors are investigated relating to poor intermetallic (IMC) formation in the Cu wirebond and bond shear force. Optical microscopic image analysis of Cu bonds, bond contact areas and Al “splash” are studied for correlation with the shear test results. Percent IMC coverage of bond contact areas decrease when invasive probe marks are present beneath the bond, which in turn may reduce the shear force. Probe mark features are studied to discover the characteristics of greatest influence on % IMC coverage and shear test values in each of the pad metal thicknesses.

Lewis Acid/Base Reactions of the Bis(amidinato)silylene [iPrNC(Ph)NiPr]2Si and Bis(guanidinato)silylene [iPrNC(NiPr2)NiPr]2Si with ElPh3 (El = B, Al)

The bis(amidinato)silylene [iPrNC(Ph)NiPr]2Si and the analogous bis(guanidinato)silylene [iPrNC(NiPr2)NiPr]2Si react with the Lewis acids BPh3 and AlPh3 to form the respective Lewis acid/base adducts 4–7 (adduct 4 has already been described). Compounds 5 and 7 are the first silylene–alane adducts and the first five-coordinate silicon(II) compounds with an Si–Al bond, and 6 and 7 represent the first silylene–borane and silylene–alane adducts, respectively, that are derived from a bis(guanidinato)silylene. Compounds 4–7 were characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy (11B, 15N, 27Al, 29Si), and 4 and 5 were additionally studied by NMR spectroscopy in solution (1H, 11B, 13C, 27Al, 29Si).

Theoretical study of isomerism in nitrogen- and phosphorus-substituted aluminum clusters M6Al38 and M12Al32 (M = N, P)

More than 20 М6Al38 isomers and several М12Al32 isomers for nitrogen- and phosphorus-substituted clusters with six and twelve dopant atoms M = N and P substituted for Al atoms in different positions at the surface of the aluminum cage and inside it have been studied by the density functional theory method. In the preferred N6Al38 isomer, all N atoms are substituted for Al atoms initially located in one outer layer of the cluster. In the course of geometry optimization, the nitrogen atoms are incorporated into positions in the neighboring intermediate layer, thus converting it into a 12-atom face consisting of three vertex-sharing adjacent six-membered rings with short N–Al bonds. For Р6Al38, a distribution of the dopant either in both surface layers or in the intermediate space between the surface layers and the inner core of the cluster is preferred. Optimization of alternative structures of the N12Al32 cluster with N atoms substituted for Al atoms in both outer layers is evidence in favor of the isomer in which the dopants are dispersed as separated monatomic anions N–. Together with their bridging Al atoms, these anions form the inner [N12Al14] cage with an unusual dumbbell-like structure in which the upper and lower halves are linked through N–Al bonds with the equatorial aluminum atoms. In the next low-lying isomer being ~23 kcal/mol higher on the energy scale, there is observed the “microclustering” of the dopant to form three covalently bonded diatomic dianions N22-; the latter, together with the bridging Al atoms are combined into a [N6Al6] “subcluster” inside the severely distorted outer cage. In P12Al32, the aluminum cage is subjected only to moderate distortions: the phosphorus atoms remain in the outer layers and form two three-membered rings [Р3]. The estimated energies of the model substitution reactions Al44 + M6 → M6Al38 + Al6 (1) and Al44 + 2M6 → M12Al38 + 2Al6 (2) demonstrate that all these reactions are exothermic; however, for the nitrogen-containing clusters, the decrease in energy with increasing number of substitutions increases from 66 (1) to 113 (2) kcal/mol, while in the case of phosphorus, it decreases from 45 (1) to 4 (2) kcal/mol. The results obtained for N6Al38, N12Al32, Р6Al38, and Р12Al32 are compared with the previous calculations for the C6Al38, C12Al32, Si6Al38, and Si12Al32 clusters.

Substituent effect on the structure and properties of dialumene

In this work, we report a theoretical study on molecular structure, and electronic properties of dialumene (ArAl = AlAr, Ar = aryl) and substituted dialumene. The effects of the substituent groups on the structure, electronic properties, ionization potential (IP), electron affinity (EA), and reorganization energy were studied. Theoretical calculations were carried out by density functional theory (DFT) using the B3LYP hybrid function combined with the 6-311 + G(d) basis set. The most intensity electronic transition energy and oscillator strength of molecules were calculated by time-dependent density functional theory (TD-DFT) and shows λmax blue-shifted in withdrawing electron substituents. Quantum theory of atom in molecules was used for explain of AlAl and AlC bonds in all molecules.

The feasibility of Sn, In, or Al doped ZnSb thin film as candidates for phase change material

The potentials of Sn, In, or Al doped ZnSb thin film as candidates for phase change materials have been studied in this paper. It was found that the Zn-Sb bonds were broken by the addition of the dopants and homopolar Zn-Zn bonds and other heteropolar bonds, such as Sn-Sb, In-Sb, and Al-Sb, were subsequently formed. The existence of homopolar Sn-Sn and In-In bonds in Zn50Sb36Sn14 and Zn41Sb36In23 films, but no any Al-Al bonds in Zn35Sb30Al35 film, was confirmed. All these three amorphous films crystallize with the appearance of crystalline rhombohedral Sb phase, and Zn35Sb30Al35 film even exhibits a second crystallization process where the crystalline AlSb phase is separated out. The Zn35Sb30Al35 film exhibits a reversible phase change behavior with a larger Ea (∼4.7 eV), higher Tc (∼245 °C), better 10-yr data retention (∼182 °C), less incubation time (20 ns at 70 mW), and faster complete crystallization speed (45 ns at 70 mW). Moreover, Zn35Sb30Al35 film shows the smaller root-mean-square (1.654 nm) and less change of the thickness between amorphous and crystalline state (7.5%), which are in favor of improving the reliability of phase change memory.

Heavily Yb-doped silicate glass thick films

A series of Yb-doped glass films has been prepared by sol–gel processing within the SiO2–Al2O3–P2O5–Yb2O3 system with doping levels up to 30 mol% Yb on a cation basis, with a thickness up to ~36 μm. The refractive indices at 633 nm, measured by spectroscopic ellipsometry, varied between 1.457 and 1.577, depending on the composition. Infrared (IR) and Raman spectroscopies were used to establish the main structural features of the different compositions, which included the presence of mixed Si–O–Al bonds evidenced by a IR peak at 940 cm−1, as well as P=O bonds revealed by a Raman peak at 1326 cm−1. The photoluminescence spectrum of Yb3+ ions was dominated by peaks at 987 and 1020 nm, with a lifetime between ~0.5–1.0 ms.

Bond coatings with high rumpling resistance: Design and characterization

Abstract The behavior of two new high-strength γ'-Ni3Al-base bond coats have been compared to a baseline β-(Pt,Ni)Al bond coat via thermal cycling to a maximum temperature of 1204 °C. The rumpling amplitude of the γ' coating is significantly lower than the (Pt,Ni)Al as characterized by a nondestructive optical profilometry technique. The γ' coatings resist rumpling and spallation of the thermally grown oxide in spite of faster oxidation compared to Pt-modified NiAl. This behavior is analyzed using an analytical rumpling model to explain that the improved bond coat strength is the major contributing factor to rumpling inhibition.

Theoretical study of isomerism of carbonand silicon-substituted aluminum clusters M6Al38 and M12Al32

More than twenty M6Al38 isomers and several M12Al32 isomers of carbon- and silicon-substituted aluminum clusters with six and twelve dopant atoms of general formula MnAl44–n(M = C and Si, n = 6 and 12) have been studied by the density functional theory method. Calculations predict that, in the lowest-lying M6Al38, isomer, all substitutions of C atoms for Al are localized in one outer surface layer of the aluminum cage. In the course of optimization, the C atoms with a negative charge of about 1e are incorporated into positions of the intermediate layer to transform it into a 12-atom face composed of three adjacent vertex-sharing six-membered rings with short C–Al bonds. In the favorable isomer of M6Al38, the dopants are scattered as individual Si atoms located in both outer layers or in the subsurface space between the outer layers and the inner core of the cluster. Optimization of low-lying isomers with twelve starting substitutions of C and Si for Al in both outer layers has localized two preferable C12Al32 isomers. One of them contains three covalently bonded diatomic C2 anions, which are combined through bridging aluminum atoms in the three-dimensional [C6Al7] cluster inside the severely distorted outer cage. In the second, most favorable, isomer, the dopants are distributed as isolated C anions; together with the bridging Al atoms, they form the [M12Al32] inner cage with an unusual dumbbell-like structure. For M12Al32, the aluminum cage undergoes moderate distortions. The silicon atoms remain in the outer layers and form five-membered ring subclusters [Si5] and [Si2Al3] bound to the neighboring intermediate layers through elongated and weakened Si–Al bonds. Evaluation of the energies of the model exchange reactions Al44 + M6 → M6Al38 + Al6 and Al44 + 2M6 → M12Al32 + 2Al6 shows that for M= C both reaction are exothermic, whereas for M = Si the former reaction is nearly isothermal and the second reaction is endothermic and requires significant energy inputs. The differences between the equilibrium structures and the relative positions on the energy scale of the isomers of the C6Al38–Si6Al38 and C12Al38–Si12Al38 clusters are examined.

Influence of Nano-Structured Silanols on the Microstructure and Mechanical Properties of A4047 and A359 Aluminum Casting Alloys

Minor alloying elements present in aluminum silicon-based casting alloys, such as sodium, strontium, or boron–titanium, could eventually affect the alloy’s microstructure and hence its mechanical properties. However, difficulties in balancing strength, ductility, and the subsequent precipitation strengthening heat treatment remain. The effects of nano-structured silanols based on partially condensed polyhedral oligomeric silsequioxanes (POSS-silanol) on the microstructure and mechanical properties of A4047 and A359 aluminum alloys were studied using a “two-step” process technique. The silanols react with active aluminum surface to form stable Si–O–Al bonds, while cage-like POSS core enables control of subsequent solidification process leading to desired mechanical performance. Using standard casting approach, the increase of both ductility and the tensile strength of the A4047 and A359 alloys is due to a highly refined fine fibrous of eutectic Al–Si formed instead of the irregular flakes as well as a refined primary aluminum phase as compared to the unmodified alloys. It has been found that this newly developed approach can also be expanded to other heat-treatable casting aluminum alloys with specific interest on changes in the microstructure of both primary aluminum phase and eutectic constituent.

Reactivity of a Monomeric Aluminium Hydrazide towards Isocyanates and Isothiocyanates: Active Lewis Pair Behaviour versus Classical Insertion Reactions

Hydroalumination of H10C5N–N=C(Ad) with HAliBu2 yielded the hydrazide H10C5N–N(AliBu2)Ad (4; Ad = adamantyl, NC5H10 = piperidinyl). Compound 4 is monomeric and contains a highly strained AlN2 heterocycle formed by a donor–acceptor interaction between the Al atom and the β‐N atom of the hydrazine. Two equivalents of the hydride afforded an adduct with an HAliBu2 molecule coordinated to 4 by an Al–N and a 3c–2e Al–H–Al bond (5). tBuN=C=O did not insert into the relatively weak Al←N donor–acceptor bond of 4; instead, insertion into the shorter Al–N(amide) bond yielded five‐membered AlN3C heterocycle 6 with an exocyclic C=O group. PhN=C=O showed a similar reaction, but the product 7 was dimeric in the solid state with two Al–O bonds. Reaction in a 1:2 ratio afforded a unique linear dimer of phenyl isocyanate, which is stabilised by the aluminium hydrazide (8). Isothiocyanates gave thiosemicarbazides 9–11, which have Al atoms coordinated in a chelating manner by formation of AlSCN heterocycles and show fascinating differences in their bonding situation.

N-type conductivity in Si-doped amorphous AlN: an ab initio investigation

We report the electronic structure and topology of a heavily Si-doped amorphous aluminium nitride (Al37.5Si12.5N50) using ab initio simulations. The amorphous Al37.5Si12.5N50 system is found to be structurally similar to pure amorphous aluminium nitride. It has an average coordination number of about 3.9 and exhibits a small amount of Si–Si homopolar bonds. The formation of Si–Al bonds is not very favourable. Electronic structure calculations reveal that the Si doping has a negligible effect on the band gap width but causes delocalization of the valence band tail states and a shift of the Fermi level towards the conduction band. Thus, amorphous Al37.5Si12.5N50 alloys show n-type conductivity.

Accelerated crystallization of zeolites via hydroxyl free radicals.

In the hydrothermal crystallization of zeolites from basic media, hydroxide ions (OH(-)) catalyze the depolymerization of the aluminosilicate gel by breaking the Si,Al-O-Si,Al bonds and catalyze the polymerization of the aluminosilicate anions around the hydrated cation species by remaking the Si,Al-O-Si,Al bonds. We report that hydroxyl free radicals (•OH) are involved in the zeolite crystallization under hydrothermal conditions. The crystallization processes of zeolites-such as Na-A, Na-X, NaZ-21, and silicalite-1-can be accelerated with hydroxyl free radicals generated by ultraviolet irradiation or Fenton's reagent.

Formation mechanism and crystal simulation of Na2O-doped calcium aluminate compounds

Calcium aluminate clinkers doped with Na2O were synthesized using analytically pure reagents CaCO3, Al2O3, SiO2 and Na2CO3. The effects of Na2O-doping on the formation mechanism of calcium aluminate compounds and the crystal property of 12CaO·7Al2O3 (C12A7) cell were studied. The results show that the minerals containing Na2O mainly include 2Na2O·3CaO·5Al2O3 and Na2O·Al2O3, when the Na2O content in clinkers is less than 4.26% (mass fraction). The rest of Na2O is mainly doped in 12CaO·7Al2O3, which results in the decrease of the crystallinity of 12CaO·7Al2O3. The crystallinity of 2Na2O·3CaO·5Al2O3 is also inversely proportional to the Na2O content in clinkers. The formation processes of 2Na2O·3CaO·5Al2O3 and 12CaO·7Al2O3 can be divided into two ways, which are the direct reactions of raw materials and the transformation of CaO·Al2O3, respectively. The simulation shows that the covalency of O—Na bond in Na2O-doped 12CaO·7Al2O3 cell is weaker than those of O—Ca and O—Al bonds. The free energy of the unit cell increases because of Na2O doping, which results in the improvement of chemical activity of 12CaO·7Al2O3. The leaching efficiency of Al2O3 in clinker is improved from 34.81% to 88.17% when the Na2O content in clinkers increases from 0 to 4.26%.

New observation of nanoscale interfacial evolution in micro Cu–Al wire bonds by in-situ high resolution TEM study

Three types of interfacial nanostructure are identified in as-bonded Cu–Al bonds: (1) Cu/~5nm amorphous alumina layer/Al; (2) Cu/~20nm CuAl2 intermetallic particle/Al; and (3) Cu/Al. During annealing, in the areas of latter two types where alumina layer is fragmented, Cu9Al4 and CuAl form as second and third intermetallic layers, and grow vertically and fast together with initial CuAl2. In the area of first type where alumina layer is present, CuAl2 grows laterally and slowly via Cu diffusion through intermetallic compounds in the neighboring area where alumina is broken to reach Al. Cu–Al interdiffusion is dominated by Cu diffusion.